This invention relates generally to a wind driven turbine generator. Particularly, the invention relates to a turbine generator constructed and arranged to increase efficiency relative to standard wind turbine designs. The turbine generator of this invention assembly utilizes a bladed wheel having a larger number of shorter blades positioned at an optimal distance from the axis of rotation. The blades rotate at a predetermined angle relative to the wind flow to allow for the maximum capture of force to provide increased torque. The assembly utilizes a cowling structure mounted upwind of the turbine blades to increase power output due to the acceleration of wind flow around the cowling structure.
The general practice of obtaining energy from the wind has been known for many years, for example, since the advent of sailing vessels. Wind energy technology has evolved and currently, large three bladed wind turbines seen across the country have become the standard model for capturing wind energy for conversion to electricity. Considering rotational blade theory, the airflow effecting a section of blade is comprised of two components. Wind flow perpendicular to the blade plane of rotation is one component and which is generally uniform across the swept area of the blades. The second component, the airfoil section, relates to the rotational blade movement or spinning about an axis parallel to the wind driven air. This second or internally driven component of the relative airflow varies linearly along the length of the blade and is equal to the rate of rotation (a constant at any instance in time) and the radius of the airfoil section. The latter component requires that spinning airfoils be twisted so the blade meets the relative wind in an efficient manner. One drawback of the standard long blade designs is that when spinning at a constant rate, only a portion of the blade is creating useful torque in the most efficient manner. The area of the blade nearest the rotation axis has a very small component due to its short radius. While the outer end blade portion has a very high self induced component due to its large radial position, the twist in the blades to compensate for this effect means that the orientation of the outer section of the wind turbine blade is nearly perpendicular to the direction of the wind flow. Although this outer section creates a large amount of lift, the lifting force is also nearly perpendicular to the plane of rotation of the turbine blade. Since only the lift component in the plane of rotation is useful, most of the lift generated by this outer blade section results in overall downwind drag on the entire wind turbine apparatus.
The forces of lift and drag, as well as the torsional and vibratory effects of turbulence and wind variance across the swept area of the blade, coupled with the length of the blades requires that the blades be strong and lightweight. This consideration greatly affects the cost of producing these and other wind turbine components. Since a major concern in the renewable energy field relates to system payback in comparison to traditional energy costs, such as fossil fuel sources, high production costs can be as disadvantageous as poor efficiency.
Other prior art structures have incorporated mechanisms to increase the wind flow prior to meeting the blades by using a nozzle or constricted cowling to attempt to take advantage of the venturi effect. However, back pressure causes these mechanisms to be ineffective. Others, such as the device of U.S. Pat. No. 7,214,029, utilize a cowling to take advantage of increased airspeed flowing around an obstruction, however, this structure only attempts to harness the accelerated airflow area. It has been found that the area of increased speed is only provided in such a small fraction of the swept area and that the blades used are too short to gain an appreciable increase in power. This structure is complex, inefficient and limited in effectiveness. The wind turbine generator assembly of the present invention uses a plurality of shorter blades rotating outwardly and behind a cowling assembly to alleviate the above enumerated problems and difficulties.